Mold release agents for use in die casting



United States Patent MOLD RELEASE AGENTS FOR USE IN DIE CASTING John W.Ryznar, La Grange, Ill., assignor to Nalco Chemical Company, Chicago,Ill., a corporation of Delaware No Drawing. Application June 18, 1956Serial N0. 591,805

12 Claims. (Cl. 22-192) The present invention relates to the chemicaltreatment of metal casting molds to prevent the adherence of nonferrousmetals thereto. More particularly, it relates to new and improved moldrelease agents for use in the die casting of aluminum and aluminumalloys.

In the die casting of non-ferrous metals, such as aluminum, aluminumalloys, brass, zinc, magnesium, copper and the like, particularly Wherehigh mold compaction pressures are applied, it has been the experienceof the art that a large proportion of the castings stick to the surfacesof the metal mold making the parting operation diificult. This usuallyresults in a spoiled casting. In attempting to alleviate the problem ofmold sticking it is the practice in some foundries to apply mold releaseagents to the faces of the mold in an effort to minimize or reduce thenumber of spoiled castings.

For a mold release agent to be effective it must give satisfactoryresults at elevated temperatures and under conditions of extremepressures. In the casting of aluminum and aluminum alloys for instance,the temperature of the molten metal usually ranges from l190 to 1450 F.It is also the practice of most casting plants to preheat and maintainthe mold temperature at 200 F. or

more.

Mold release agents now employed in die casting operations are composedof a wide range of ingredients and may contain several of the followingchemical agents; various mineral oils, graphite, petroleum and naturalwaxes, molybdenum sulfides, heavy metal soaps and chlorinated aliphaticsolvents. While in some instances satisfactory results have beenobtained using presently known mold release agents they do not alwaysoperate to al-. leviate one or more of the following undesirable conditions: 7

A. Staining of the casting (carbonizing), particularly where oil-basedformulas containing graphite or molybdenum sulfides are used; 7 V r V B.Inadequate lubn'cation resulting in the sticking of the casting'to thedie which interrupts the manufacturing procedure;

C. Metal porosity caused by entrapmentof the gases resulting fromburning oil contained in the formulas;

D. Surface imperfections (flowers), injconsequence of excessive amountsof release agent on the mold, and

ful in the die casting of aluminum and aluminum alloys.

A further object is to provide a mold release agent for metal castingmolds which will prevent carbonizing, flowering and provide lubricationto the die. w 7

Yet another object is to furnish a mold release agent for metal castingmolds which is easily applied andwill last for more than one castingoperation. Other objects will appear hereinafter. v V

In accordance with the invention it has been found that non-ferrousmetal castings can be prevented from adhering to the surfaces of themetal molds in which they are cast by applying to the surfaces of suchmolds a uniform thin coating of a hydrocarbon polymer of anunsubstituted, monoolefinic, aliphatic monomer. Particularly goodresults are afforded-when the non-ferrous metal is aluminum or an alloyof aluminum.

The hydrocarbon polymer of an unsubstituted monoolefinic, aliphaticmonomer may be prepared from any number of hydrocarbon monoolefinsincluding crude mixtures containing substances other thanhydrocarbonproviding such mixtures do not contain major amounts of monomers havingfunctional substituents such as halogen groups, carboxylic acid groups,nitrile groups or other similar groups. The starting monomer or theresulting polymer may contain branched chain hydrocarbon groups such asmethyl or ethyl groups. The polymer may contain minor amounts of keto,aldehyde or carboxylic acid groups which result from oxidation processesto which some of the hydrocarbon polymers are subjected.

Preferred hydrocarbon polymers are those derived from such low molecularweight olefins as ethylene, propylene, butylene, isobutylene and thelike. Higher molecular weight monoolefins, such as are derived frompetroleum may also be used but due to their unavailability and lack ofchemical purity they are not entirely satisfactory.

While any hydrocarbon polymer within the prescribed class may be used itis necessary that it is capable of being applied to the mold face in athin, uniform coating. The thickness of the coating is desirably around0.000001 to 0.001 inch, preferably about 0.0001 inch. Excess polymer orpartially adhering polymer particles on the mold face will tend to givea poor quality casting. If, however, the hydrocarbon polymer isuniformly coated onto the mold in a thin film, outstanding mold'releaseproperties are achieved.

It has been found in the practice of the invention that certain lowmolecular weight hydrocarbon polymers can E. The application of the moldrelease agents after each casting operation in order to operate at peakefchemical treatment for metal casting molds to prevent the adherence ofnon-ferrous metals thereto.

7 Another object is to provide a mold release agent use- 'be easilyapplied to casting molds in a molten state or from a liquid vehicle andform, a thin, uniform coating on the mold surfaces. These low molecularweight hydrocarbon polymers preferably have an average molecular weightof ,at least 300 and not in excess of about 5000. In a desirableembodiment polyethylenes and polyisobutylenes having an averagemolecular weight in the range of 300 to 2000 give outstanding results.The polyisobutylenes available commercially are derived by reactingcertain olefinic cuts of petroleum fractions., ,They may be consideredas mixtures of polyisobutylenes, polybutylcues and minor portions ofaliphatic components such as parafiins. For the sake of convenience theywill hereinafter be referred to simply as polyisobutylenes.'Polyethylenes having an average molecular weight of 1500 to 2000 havegiven very good results. also been obtained with polyisobutylenes havingan average molecular weight from about 300 to about 1000. For purposesof illustrating some of the preferred hydrocarbon polymers severalpolyethylenes and polyisobutylenes are listed below in Table I.

Good results have- TABLE 1 Average Molecular Weight Composition N0.Polymer Polyethylene ,rln

Polyisobutylene 1 Oxidized material containing minor amounts of carbonylgroups.

In the above table the various polyethylenes are soft, waxy solidsmelting between 88 C.106 C. The polyisobutylenes are usually viscousliquids.

'It is usually desirable to suspend or disperse the hydrocarbonpolymers, such as those described above, in a suitable organic liquid.Such dispersions are admirably suited for application to metal castingmolds since they can be applied by spraying, brushing or other similarexpedients.

Dispersions employing the compositions listed in Table I can be preparedby using such organic liquids as kerosene, mineral seal oil, benzene,toluene, xylene, alkyl substituted benzenes, chlorinated aromaticcompounds, carbon tetrachloride, trichloroethylene and suitablehydrophobic solvents derived from petroleum. The criteria for a suitableorganic liquid are that under conditions for use it must be volatile,non-carbonizing and must uniformly wet the surface of the mold so thatlocal concentrated zones of liquid or hydrocarbon polymer do not form.In choosing the proper organic liquid much will depend on the conditionsunder which it will be employed.

From the standpoint of practical formulation the dispersions generallycontain from 2% to 30% by weight of the hydrocarbon polymer andpreferably to by weight. A single hydrocarbon liquid vehicle orcombinations of vehicles may be used in the formulation.

When hydrocarbon polymers such as polyethylene are employed thedispersions are readily prepared by melting the polyethylene and addingit in a liquid state to the organic liquid which is preferably heated.In the casting of aluminum and its alloys a good hydrocarbon liquid forthe low molecular weight polyethylenes is kerosene.

In order to illustrate several typical dispersions of polyethylenes andpolyisobutylenes in organic liquid the following compositions are listedbelow in Table II. Where polyethylenes were used they were first meltedand then added to the organic liquids.

TABLE H Percent y Weight Composi- Cornposltlon No. tioInITaIble OrganicL1quid(s) Puriged Kerosene.

o. 30% dodecyl benzene. 35% tetrahydronaphthalene. 26%trichloroethylene. Purified Kerosene. Odorless Kerosene.

1 Thick translucent jelly.

are generally preferred since they are capable of being readilyemulsified in aqueous media.

Emulsions of Compositions I to XI in aqueous vehicles may be preparedusing several well known emulsifying 5 agents such as aliphatic and/orheterocyclic amines and fatty acids. A typical emulsion is listed below:

Composition XVII Ingredients: Percent by weight Composition IV 20 Oleicacid 4 Morpholine 4 Water 72 In order to evaluate several compositionsof the invention tests were run to determine the effectiveness of thematerials on a commercial die casting machine under actual operatingconditions. The conditions of the test were as follows:

EXAMPLE Aluminum metal was kept molten at 1200:25 F. in a gas furnaceand was hand ladled into a Kux zinc die casting machine which wasconverted to aluminum casting. The die consisted of four major pieces,two side pieces containing bores being moved into position by sliding ina slot and actuated by slanted rods as the diehalves closed. The taperon cores (die pieces mostly surrounded by casting) and parts whichrequired withdrawal from the die was from one to five degrees. Eightquarter-inch and 3 three-sixteenth inch diameter ejector pins were usedto remove the castings under test from the die. As the molten metalentered the die a hydraulically actuated plunger under about 300 poundsper square inch of pressure was released a distance of eighteen inchesand rammed the molten metal into the interstices of the mold cavity. Thetemperature of the mold was maintained at about 400 F.

There were numerous variables which could only be controlled by theoperator but by and large mold release agents that were used in themachine prior to the compositions of the invention caused many poorcastings to be produced. The compositions tested were applied to themold by either brushing, spraying or trowelling depending on the formulatested and the equipment available for applications. The results ofseveral of these tests are listed below in Table III:

TABLE 111 No. of Mold Castings Composition Tested Release Made Be-Remarks Obtained fore Reapplication XVII Good. 4 N0 staining present.XII o. 3 Sticking when die kept hot and not operating withoutreapplication.

XIII do 2 Excess of material did not produce flowers.

XIV .do When excessive amounts are applied staining occurs.

XV do Operator deemed results to be excellent.

XVI do.. 2 When excessive amounts are applied flowers produced.

Commercial Agent: Poor.... One in five castings Oil Base fouled.

Usually for optimum results to be obtained the compositions must beapplied in a uniform coat. When the material is applied in blotches poorcastings result even though mold release is achieved. When uniformlyapplied the compositions of the invention provide excellent mold releaseand high quality castings. When solid hydrocarbon polymers are used theymay be applied in any form and by any means, such as flame spraying solong as a uniform coating is placed on the surface of the mold.

It is important to. choose organic liquid dispersants 75 which underconditions of use will uniformly volatilize Without leaving carbonaceousresidues. It is believed the low molecular weight hydrocarbon polymersare particularly effective due to their ability to slowly difiuse in agaseous state without leaving any residual carbonaceous deposits.

It will be understood that although good results are obtained by usingindividual hydrocarbon polymers alone and in various physical forms,satisfactory results may be obtained by blending two or more of thepolymers in any practical proportions.

The metal casting molds are usually made of ferrous metals, e.g., castiron and steel. In the past, many metal casting molds have been made ofcast iron and have steel cores. Many molds are made of cold rolledsteel.

In all the tests conducted with the compositions herein describedcasting stain was abolished or greatly mitigated. This is highlysignificant when it is understood this is the worst problem usuallyencountered in the use of conventional mold release agents.

The invention is hereby claimed as follows:

1. The method of casting a non-ferrous metal which comprises coating themetal face surfaces of a metal mold with a uniform thin coating of ahydrocarbon polymer of an unsubstituted, monoolefinic aliphatic monomer,said polymer having an average molecular weight not greater than 5000,and casting said metal in said coated mold.

2. The die casting method which comprises providing the metal facesurfaces of a ferrous metal die with a uniform coating having athickness in the range of about 0.000001 inch to 0.001 inch of a polymerfrom the group consisting of polyethylene and polyisobutylene, saidpolymer having an average molecular weight in the range of 300 to 5000,casting a molten metal from the group consisting of aluminum andaluminum alloys in said die, and separating the casting from the die.

3. The method of claim 1 wherein said polymer is selected from the groupconsisting of polyethylene and polyisobutylene having an averagemolecular weight in the range of from 300 to 5000.

4. The method of claim 1 wherein said non-ferrous metal is selected fromthe group consisting of aluminum and aluminum alloys.

5. The method of claim 4 wherein said polymer is selected from the groupconsisting of polyethylene and polyisobutylene having an averagemolecular weight in the range of from 300 to 5000.

6. The method of claim 1 wherein said polymer is applied to said molddispersed in a volatile non-carbonizing organic liquid.

7. The method of claim 1 wherein said polymer is applied to said molddispersed in an aqueous vehicle containing an emulsifying agent.

8. The method of claim 7 wherein said polymer is polyethylene having anaverage molecular weight in the range from 1500 to 2000.

9. The method of casting a non-ferrous metal selected from the groupconsisting of aluminum and aluminum alloys which comprises coating themetal face surfaces of a ferrous metal mold with a uniform thin coatingof a dispersion of a hydrocarbon polymer selected from the groupconsisting of polyethylene and polyisobutylene in a volatilenon-carbonizing organic liquid, said polymer having an average molecularWeight in the range of from,

300 to 2000, and casting said metal in said coated mold.

10. The method of claim 9 wherein said polymer is polyethylene having anaverage molecular weight in the range from 1500 to 2000.

11. The method of claim 9 wherein said polymer is polyisobutylene havingan average molecular weight in the range from 300 to 1000.

12. The method of claim 9 wherein said organic liquid is kerosene.

References Cited in the file of this patent UNITED STATES PATENTS2,092,296 Voorhees Sept. 7, 1937 2,153,553 Fawcett et al Apr. 11, 19392,326,955 Mack Aug. 17, 1943 2,335,930 Freeland et a1. Dec. 7, 19432,406,039 Roedel Aug. 20, 1946 2,488,446 Swiss Nov. 15, 1949 2,629,907Hugger Mar. 3, 1953 2,695,246 Jurgensen et al Nov. 23, 1954 FOREIGNPATENTS 543,577 Great Britain Mar. 4, 1942 585,395 Great Britain Feb. 6,1947'

1. THE METHOD OF CASTING A NON-FERROUS METAL WHICH COMPRISES COATING THE METAL FACE SURFACES OF A METAL MOLD WITH A UNIFORM THIN COATING OF A HYDROCARBON POLYMER OF AN UNSUBSTITUTED, MONOOLEFINIC ALIPHATIC MONOMER, SAID POLYMER HAVING AN AVERAGE MOLECULAR WEIGHT NOT GREATER THAN 5000, AND CASTING SAID METAL IN SAID COATED MOLD. 